The present invention relates to a method for producing novel molybdenum-containing supported catalysts and to a process for oligomerizing unsaturated hydrocarbons having 2 to 5 carbon atoms in the molecule in the presence of the novel catalysts.
It is known from Asinger, "Die Petrolchemische Industrie" volume I, pp. 275 (1971) to oligomerize lower olefins with acids or acid-containing catalysts. In this connection, phosphoric acid or phosphoric acid-containing catalysts have proven to be preferable. However, acidic catalysts have the disadvantage of being sensitive to sulfur, ammonia, amines and acetylene, thereby requiring that such substances be substantially removed from the gaseous olefins prior to oligomerization. In addition, when the reaction conditions during oligomerization of olefins with acids are not closely adhered to, considerable amounts of non-olefinic by-products are obtained as a result of hydropolymerization.
Furthermore, it is known to perform selective di-, tri- and polymerization of certain lower olefins employing such catalysts as, for example, Ziegler-Natta catalysts and catalysts comprising cobalt on activated carbon as well as with alkali metals and aluminum chloride. Moreover, a number of other metals were tested with regard to their activity as oligomerization catalysts including, for example, a supported MoO.sub.3 catalyst. Such catalysts, however, preferably disproportionate olefins. Thus, for example, from 2 molecules of propylene essentially butene and ethylene are obtained and only a small amount of propylene is oligomerized to C.sub.6 -hydrocarbons.
U.S. Pat. No. 2,446,619 suggests to use the oxide of molybdenum and phosphoric acid on a suitable support, such as silica gel, as catalyst for oligomerization where the dimerization of lower olefins is preferred. The reference reports that in the absence of hydrogen and utilizing a temperature of about 550.degree. to 600.degree. F. and a pressure of 200 p.s.i.g. only 12 weight percent of liquid product basis the olefin feed was provided. The addition of hydrogen to the gaseous olefins raised the liquid product to 25.7 weight percent. Similar results are reported with another modified molybdenum-containing carrier catalyst.
According to U.S. Pat. No. 2,446,619, a plurality of materials are suggested as catalysts. One type includes variable valent metals active for the hydrogenation and dehydrogenation, e.g. tungsten, vanadium, molybdenum and chromium, used in the oligomerization catalyst in the form of an oxide or sulfide. Since no further mention or examples are provided regarding the sulfides, this suggests that catalysts containing, for example, molybdenum sulfide are less effective than catalysts containing molybdenum oxide. Our experiments with catalysts containing molybdenum sulfide showed that such catalysts are practically inactive for both the oligomerization and the disproportionation of unsaturated hydrocarbons having 2 to 5 carbon atoms in the molecule.
It is an object of this invention to provide a process for oligomerizing unsaturated hydrocarbons in high yields.
Another object of this invention is to provide a new catalyst for oligomerizing unsaturated hydrocarbons having 2 to 5 carbon atoms in the molecule.
Another object of this invention is to provide an oligomerization process wherein C.sub.2 to C.sub.5 unsaturated hydrocarbons are selectively converted to higher olefinically unsaturated hydrocarbons where said process produces essentially no saturated by-products by hydropolymerization.
Yet another object is to provide a catalyst that is substantially insensitive to sulfur, ammonia, amine or acetylene components in the olefin feedstock.
Other objects and advantages will become apparent from a reading of the following detailed description and examples.